The present invention relates generally to photovoltaics (PV) and more specifically to concentrator photovoltaic modules as well as methods for making such modules.
Generating electricity directly from sunlight by the irradiation of semiconductor materials has been the subject of investigation for a number of decades without great commercial success. Simply stated, the cost of generating electricity in this manner is not cost effective except in rare specialized circumstances.
Photovoltaic converters can be classified in two general categories: those that use lens concentrators and those that do not. By the use of lens concentrators the amount of sunlight directed to a cell can be multiplied many times. Concentrator PV modules have inherent problems of their own, however, which often make their use questionably efficient. For example, while the heat generated by the sun on cells without concentrators can be dissipated by convection sufficiently to allow the system to operate at tolerable temperatures, the same is not true of cells with concentrators which require supplemental cooling. Although pump driven fluid cooling provides a solution to the heat problem, the initial capital cost, the cost of operation and the complexities attendant fluid cooling systems detracts from the overall economics. In addition, the housings that support concentrator lenses which typically have focal lengths of 6-12 inches or more, and the fluid cooling plumbing create apparatus which is massive and thus difficult and expensive to deploy and adopt to sun tracking mechanisms.
Heat losses are also experienced as a result of current flowing in semiconductor surfaces (I.sup.2 R heat). To reduce this problem it is common practice to overlay sheets of semiconductor material with a mesh of fine conductors to reduce the distance that current must travel in the semiconductor material and thus reduce resistance heating losses. This mesh structure, however, is located between the cell and the sunlight and thus reduces the area of semiconductor material that receives light. In addition, if the mesh structure is made too fine, production yield becomes unacceptable. This so-called shadow effect can be significant and forces a trade-off between losses due to resistance (I.sub.2 R) and the amount of material irradiated. Further, the resistance of the fine wire conductors creates even further resistance losses.